I like the LDK a lot. The performance is pretty much on par with the Caanoo, but it doesn't seem to really outperform it on any point. The lack of a touch screen doesn't come up *that much* for me, but it's something to keep in mind. I'll still be relying on an android device (Shield Handheld) for PSX, etc.
My decrepit hands don't do so hot with the shape of it. It's a top-heavy design, and my thumbs start to ache after half an hour of use. Working to keep the system balanced in your hands makes more of a difference than you might think.
The manufacturers seem to sell basically the same hardware in tons of different form factors. It's all built around the same chip family as the Neo Geo X and the Neo Mini cabs. The rs-90, which has more of a DMG-style body, looks much more comfortable to hold, especially since it moves the L and R buttons to the back of the device, instead of the top. But it's only got the two face buttons, so it's a clear trade off. The rs-07 is basically the Neo Mini Arcade with six buttons. Shop around, read the dingoonity forums, and see where the community developers are with the device you're considering, because that's ultimately going to determine what you'll be able to do with it.
I've seen a picture of a rumored redesign (which looks pretty much exactly like the rs-97 plus. For all I know, it *is* exactly the same device) which I think would be a lot more comfortable to hold and use.
For $50, the LDK is a great deal. If you aren't in a rush, you might want to wait for another revision or look at some of the other devices that are currently available.